1. Field of the Invention
This invention relates to a water-soluble electrically-conductive polyaniline and a method for the production thereof. The aqueous solution of the water-soluble electrically-conductive polyaniline is useful for preparing a commercially acceptable thin films by such a simple procedure such as spin coating, dip coating, or bar coating. The water-soluble electrically-conductive polyaniline can be utilized for various antistatic devices, transparent electrodes, shields against electromagnetic radiation, photovoltaic elements, organic electroluminescent elements, organic electrochromic elements, corrosion inhibitors, semiconductor photocatalysts, photoresists, nonlinear optical materials, and the like.
This invention further relates to an antistatic agent using a water-soluble electrically-conductive polymer. The aqueous solution of the antistatic agent is useful for preparing commercially acceptable thin films with fast and strong adhesion to polymer films, polymer fibers, and moldings of polymer resins by a simple procedure such as spin coating, dip coating, or bar coating. Further, the antistatic agent manifests excellent antistatic effects even under low humidity.
2. Description of the Prior Art
First, since the doped polyaniline is stable as an electrically-conductive polymer and derives from inexpensive raw materials, the development of the applications thereof to film electrodes, secondary batteries, capacitors, antistatic agents, shields against electromagnetic radiation, etc. is being promoted. However, the insoluble and infusible character of polyaniline prevent easy formation or fabrication. The solubilization of the polyaniline, therefore, is significant from the commercial point of view. From the standpoint of handling in a factory, solubility in water provides many advantages over solubility in other solvents.
Second, since polymer films, polymer fibers, moldings of polymer resin, etc. are electrical insulators, they tend to buildup static electricity to the extent of breaking electronic components, attracting dust, and possibly causing a fire. Thus, a solution of these issues is essential. Heretofore, surfactants have been mainly used as antistatic agents. Since surfactants show ionic conduction by moisture in the air, it is difficult to lower the surface resistance below 10.sup.9 (.OMEGA.,.quadrature.) and still keep the antistatic effect tinder the condition of low humidity.
Another electron-conductive antistatic agent has also been known, where carbon black, fine powder of metals such as aluminum, copper, or silver, and fine powder of semiconductors such as indium tin oxide or fluorine-doped tin oxide are dispersed as fillers in a general-purpose polymer. Using these fillers, however, causes problems such as (1) fairly large amounts of fillers are required, (2) controlling the electric resistance is difficult because the electric resistance may suddenly decrease at certain amounts of filler addition, (3) the fillers will gradually come out to the surface of a coating film with age, preventing the film from acquiring a smooth surface, (4) the film has inferior transparency, and (5) the strength of the coating film is low.
Though the electrically-conductive polymers have a bright prospect of solving these problems, they are generally at a disadvantage in being neither moldable nor processible because of their insolubility and infusibility. The doped polyaniline, among other electrically-conductive polymers, features stability in the air, inexpensiveness of the raw materials and suitability for the development of applications. Polyaniline is insoluble and infusible, however, like other electrically-conductive polymers. Therefore, the solubilization of polyaniline is commercially significant. From the view points of handling in a factory, using water to dissolve polyanitive provides many advantages such as cost and safety compared to using organic solvents.
For the doped polyaniline which is useful for film electrodes, secondary batteries, capacitors, antistatic agents, shields against electromagnetic radiation, etc. and for the electrically-conductive polymers, particularly the doped polyaniline, which are useful for polymer films, polymer fibers, molding of polymer resin, etc., the necessity for improving the solubility of polyaniline in water has been getting attention.
For the purpose of improving the solubility of polyaniline in water, various methods for the introduction of a sulfonic group to the polyaniline have been proposed in recent years. Methods for polymerizing aminobenzene sulfonic acid as a monomer have been known such as, for example, synthesizing sulfonated polyaniline by electrochemically copolymerizing aniline with o- or m-aminobenzene sulfonic acid (Journal of Japan Chemical Society, 1985, p. 1123 and JP-A-02-166,165), copolymerizing aniline with aminobenzene sulfonic acid by chemical oxidation (JP-A-01-301,714 and JP-A-06-56,987), sulfonating the copolymer of aniline with aminobenzene sulfonic acid and a derivative thereof (JP-A-05-18, 989), polymerizing o-, m-aminobenzene sulfonic acid by electrochemical oxidation (Glossary II of Lecture Prescripts of the 64th Autumnal Annual Meeting of Japan Chemical Society, p. 706, 1992), and polymerizing o-, m-aminobenzene sulfonic acid and a derivative thereof by chemical oxidation (JP-A-07-324,132 and JP-A-08-41,320).
Further, methods for introducing a sulfonic group into the polyaniline through the medium of a sulfonating agent have been proposed such as, for example, sulfonating an emeraldine salt by the use of sulfuric anhydride/triethyl phosphate complex (JP-A-61-197,633), sulfonating undoped polyaniline (emeraldine base) by the use of fuming sulfuric acid (WO91-06887, J. Am Chem. Soc., 1990, Vol. 112, p. 2800, J. Am. Chem. Soc., 1991, Vol. 113, p 2665), sulfonating undoped polyaniline (emeraldine base) in chlorosulfonic acid (Polymer, 1991, Vol. 33, p 4410), and a method for sulfonating the polyaniline of a leucoemeraldine base with fuming sulfuric acid (J. Am. Chem. Soc., 1996, Vol. 118, p 2545).
The method for copolymerizing aminobenzene sulfonic acid and a derivative thereof with aniline by electrochemical or chemical oxidation, however, is barely capable of introducing sulfonic groups at a ratio of one sulfonic group to five aromatic rings. The product of this method, has a solubility problem because it is insoluble in water while it is slightly soluble in aqueous alkalis. Then, the method which further sulfonates such a copolymer is shown to introduce sulfonic groups at a ratio of slightly over one sulfonic group to two aromatic rings. The product of this method also has a solubility problem because it is insoluble in water though it is soluble in aqueous alkalis.
The method for polymerizing o-, m-aminobenzene sulfonic acid by electrochemically oxidation, in spite of the previous statement that the method has produced a water-soluble electrically-conductive polymer, has such problems that the method is not suitable for the manufacture on a commercial scale because the polymerization is an electrode reaction and isolation of the product is difficult. When the method for polymerizing o-, m-aminobenzene sulfonic acid and a derivative thereof in an acidic solution by chemical oxidation or a basic solution by chemical oxidation is verified, it is found to yield a reddish brown oligomer and to not form a sulfonated polyaniline in the state of an emeraldine salt as the repeating unit thereof. It is generally difficult to obtain a polyaniline of high molecular weight with green color which is characteristic for the emeraldine salt by polymerizing an aniline monomer possessing a substituent.
In the methods for introducing a sulfonic group by the use of a sulfonating agent, the method which sulfonates a polyaniline by the use of a sulfuric anhydride/triethyl phosphate complex barely introduces sulfonic groups at a ratio of one sulfonic group to five aromatic rings. The compound produced by this method, shows no solubility in water in the doped state. The method of the sulfonation by the use of fuming sulfuric acid affords a self-doped polyaniline with sulfonic groups at a rate of one sulfonic group to two aromatic rings. The polyaniline, however, is insoluble in neutral to acidic aqueous solutions because the sulfonic groups are utilized for doping the aniline. It, therefore, must react with an alkali to become soluble in the aqueous solutions. The polyaniline generally turns into an insulator when it reacts with an alkali. The self-doped polyaniline, therefore, does not fully satisfy needs of moldability and processibility because it must be redoped after processing.
The method of sulfonation by chlorosulfuric acid affords a self-doped polyaniline with four sulfonic groups per five aromatic rings. This polyaniline, however, is insoluble in neutral to acidic aqueous solutions because the sulfonic groups are utilized for doping the aniline and must react with an alkali to become soluble in the aqueous solutions. Thus, it is not suitable for processing. The method which sulfonates the polyaniline of a leucoemeraldine base with fuming sulfuric acid yields polyaniline with three sulfonic groups per four aromatic rings. Since this product is a self-doped one, it is only slightly soluble in water and is problematic in terms of solubility and processibility.
Further, in the methods of the sulfonation by the use of fuming sulfuric acid and chlorosulfuric acid mentioned above, since they use a large excess of the sulfonating agent relative to the amount of polyaniline, they have the problem of having to dispose a large amount of used acid.
Water-soluble polyanilines in the electrically conductive state have been known, including, namely in the doped state, N-sulfonated polyaniline resulting from the chemical oxidative polymerization of diphenyl amine-4-sulfonic acid (Polymer, 1993, Vol. 24, p. 158), N-propane sulfonic acid-substituted polyaniline resulting from the reaction of polyaniline with 1,3-propane sultone (J. Am. Chem. Soc., 1994, Vol. 116, p. 7939 and J. Am. Chem. Soc., 1995, Vol. 117, p. 10055), and phosphonated polyaniline resulting from oxidative polymerization of o-amino-benzyl phosphonic acid (J. Am. Chem. Soc., 1995, Vol. 117, p. 8517).
The isolation of the N-sulfonated polyaniline, however, is extremely complicated because the polymer possesses such high solubility as to necessitate high-speed centrifugation after the polymerization. Then, since the N-propane sulfonic acid-substituted polyaniline is a self-doped polyaniline and is insoluble in water in the doped state, it cannot be soluble in water in the doped state unless by a method of treating the aqueous solution of a sodium salt thereof with an ion-exchange resin. Thus, it has the problem of having no alternative but to use a very complicated procedure in terms processiblility. The phosphonated polyaniline has the problem of being unusually complicated from the commercial point of view because the production of the o-aminobenzyl sulfonic acid, the raw material for polymerization, requires several steps of reactions.
A water-soluble polyaniline in the conducting state, namely in the doped state, a method for producing this polyaniline with a simple procedure, and an antistatic agent using such a water-soluble electrically-conductive polymer as the polyaniline have never been heretofore known to the art.
The first object of this invention, therefore, is to provide a novel water-soluble electrically-conductive polyaniline and a method for the production thereof.
The first object of this invention also resides in providing a polyaniline which is soluble in water in the state having high electrical conductivity, namely in the doped state, and a method for the production thereof.
The second object of this invention is to provide, by using preferably the novel water-soluble electrically-conductive polyaniline (such as, for example, sulfonated polyaniline) mentioned above as a polymer soluble in water in the state having high electrical conductivity, namely in the doped state, an antistatic agent with lower resistance which retains the effect thereof even at and lower humidity than prevalent heretofore, excels in coating property and adhesiveness to a substrate, and enjoys fully satisfactory strength, transparency, and waterproofness after application to a surface.